1. Field of the Invention
The present invention relates to a method for controlling a damper clutch. More particularly, the present invention relates to a method for controlling a damper clutch which can effectively eliminate unusual vibration of an engine by controlling a damper clutch of a torque converter.
2. Description of Related Art
A torque converter of a vehicle such as a hydraulic torque converter includes an impeller that rotates by receiving a driving force of an engine, a turbine that rotates by a fluid discharging from the impeller, and a stator (or reactor) that increases a torque changing rate by making a return current of the impeller for heading to a rotating direction of the impeller.
In the torque converter, the impeller is fixed at and rotates with a front cover thereof which is a rotating body of an input side, and causes an inner fluid to flow to the turbine. As a result, a torque is transmitted from the rotating body of the input side to a rotating body of an output side.
Further, a damper clutch is disposed in a space between the front cover and the turbine so as to directly and selectively connect them to each other for directly transmitting torque. As a result, the damper clutch plays a role in directly transmitting rotating power of the engine to the turbine.
Particularly, as shown in FIG. 6, if the damper clutch has a 2-stage stiffness structure, unusual subharmonic vibration can occur at the boundary of the 2-stage stiffness when engine torque is inputted such that a serious problem may occur in the vehicle body.
To solve this problem, if the stiffness of the damper clutch having the 2-stage stiffness structure increases, then a large booming sound arises such that noise-vibration-harshness (NVH) of the engine becomes worse and fuel efficiency deteriorates, as shown in FIG. 6. On the other hand, if the stiffness of the damper clutch having the 2-stage stiffness structure decreases, then the booming can be improved but the unusual vibration becomes worse. Therefore there is a contradiction between booming and unusual vibration. As shown in FIG. 1, the unusual vibration range and the booming range are different such that it is difficult to solve the problem by changing stiffness of the damper clutch having the 2-stage stiffness structure.
On the other hand, if the damper clutch has a multi-stage stiffness structure so as to settle the problem, then unusual vibration and booming can be improved somewhat, but it is actually difficult to apply to the damper clutch since the multi-stage stiffness structure is embodied under some limited design conditions such as maximum torque, angle of torsion, etc.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention, and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.